1. Field of the Invention
The invention relates to an X-ray device which includes at least one radiation source, a diaphragm device with shutters, and a recording and image processing unit.
2. Description of Related Art
The X-ray dose whereto a patient is exposed during an examination by means of X-rays should be kept as small as possible. To this end, the beam is restricted by a diaphragm device. The evaluation of an X-ray image necessitates a faithful reproduction of even the smallest differences in the gray tones.
DE 195 39 602 A1 describes an X-ray examination apparatus provided with two adjustable diaphragm devices. A first diaphragm device restricts an X-ray beam which is generated by an X-ray source, traverses an examination zone and subsequently passes through a second diaphragm device before it is incident on a unit for recording the X-ray image. The second diaphragm device is constructed so that it can be seen in the X-ray image whether the X-ray beam defined by the first diaphragm device is significantly larger than the X-ray beam defined by the second diaphragm device. To this end, the shutters of the second diaphragm device are provided with indentations which extend perpendicularly to the edges of the shutters and form strip-like projections at the edge of the X-ray image. It is thus achieved that the X-ray image has a well-defined boundary, because the definition by means of the first diaphragm device only leads to unsharp edges of the X-ray image. The second diaphragm device, being arranged at a small distance from and in front of the unit for recording the X-ray image, ensures that the edges of the shutters are sharply imaged in the X-ray image.
DE 196 37 918 A1 describes an X-ray device for medical applications in which means for generating a device-specific and/or component-specific mark or data symbol are automatically assigned to an image to be formed. They concern recesses, marks or punctures which are reproduced in the image in such a manner that the images can be identified on the basis thereof during later observation by the physician; such marks can also provide the physician with additional information concerning the image.
The definition of the beam path by means of the diaphragm device produces edges in the radiation image which separate the area traversed by X-rays from the area not traversed thereby. The complete radiation image exhibits many different black-white transitions or gray tone transitions which are formed on the one hand by gray tone transitions at, for example bones, but on the other hand also by the edges of the shutters. For the evaluation of the radiation image, however, the physician requires only the exposed area. The evaluation of the overall radiation image may lead to false interpretations, because different gray tones caused by scattering are also reproduced in the non-exposed area.
Citation of a reference herein, or throughout this specification, is not to construed as an admission that such reference is prior art to the Applicant""s invention of the invention subsequently claimed.
It is an object of the invention to detect the edges of the shutters in order to reproduce only the exposed area for the observation of the radiation image.
This object is achieved in that the shutters are provided with hole and/or edge patterns which reproduce non-anatomical patterns in the radiation image and that the image processing unit is arranged to detect the shutter edges in the radiation image.
The shutters are provided with hole and/or edge patterns which do not occur in human anatomy. The shutters are arranged in the beam path of the radiation source in such a manner that the part of the patient irradiated by the rays is limited from the outside. To this end, the shutters are arranged so as to be movable in the diaphragm device. The displacement of the shutters can take place manually or also automatically by means of adjusting motors which are driven by a control circuit. The hole patterns are provided in the shutters at a known distance from the edge. The hole patterns, consisting of a plurality of holes, are transparent to radiation and hence are reproduced in the radiation image. The edge patterns are provided at the edges of the shutters and also have a non-anatomical shape which is also reproduced in the radiation image. After having passed the shutters, the radiation traverses the part of the patient to be examined. The radiation is then influenced or absorbed by the tissue and the bones of the patient, and is subsequently incident on the recording unit in which a radiation image is formed which contains on the one hand the hole and/or edge patterns and on the other hand different gray tones, since the radiation is absorbed to a different extent because of the different density of tissues and bones.
The radiation image is applied to the image processing unit. Therein the radiation image is examined for the known hole and/or edge patterns which will be referred to hereinafter merely as patterns. Because the patterns do not have an anatomical shape, mix-ups with, for example, transitions from bones to soft tissue can be precluded during the edge detection. After the known patterns have been found, the position of the edges in the radiation image is calculated on the basis of the known arrangement of the patterns in the shutters. The edges of the shutters reproduce a comparatively strong gray tone transition in the radiation image, so that it can be unambiguously identified by way of such a calculation. After the detection of the edges of the shutters, the areas of the radiation image which are situated outside these edges are suppressed and not displayed to the observer. A display unit shows the observer only the part of the patient which has been traversed by the radiation, so that for the diagnosis the observer will not include gray tone transitions caused by scattering of the radiation. The radiation dose whereto the patient is exposed is thus reduced to a necessary minimum.
In a preferred embodiment of the invention the hole pattern is realized in the form of perforations. The hole patterns are then arranged in several rows which extend parallel to the edge of the shutter. The hole patterns have a different arrangement in each row. The distances between the individual holes as well as the diameter and the shape of the holes can be varied. By using different types of perforations, the pattern thus reproduced in the radiation image can be adapted to the relevant application, so that in the case of imaging of given objects a perforation can be selected whose reproduction in the radiation image is unambiguously distinct from the imaged object and hence mix-ups are precluded during the edge detection.
In a preferred embodiment of the invention information is encoded in the perforations. When a plurality of parallel rows of perforations are reproduced in the radiation image, the magnitude of the covered area in the radiation image is encoded for example, by way of an increasing spacing of the holes in the rows of perforations. The detection of the edges in the image processing unit then yields further information as to how much surface area of the maximum possible radiation image area is covered by the shutters.